# CVE-2026-27571: GO-2026-4533 - nats-server websockets are vulnerable to pre-auth memory DoS in github.com/nats-io/nats-server

Source: https://junglewise.ai/threats/cve-2026-27571-nats-server-websockets-are-vulnerable-to-pre-auth-memory-dos  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-02-25  
License: CC BY 4.0 with a link back

CVE-2026-27571 · Severity: low · CVSS 3.1 · Published 2026-02-25

nats-server websockets are vulnerable to pre-auth memory DoS in github.com/nats-io/nats-server

Technologies: [github.com/nats-io/nats-server (Go)](https://junglewise.ai/threats/technologies/github-com-nats-io-nats-server), [github.com/nats-io/nats-server/v2 (Go)](https://junglewise.ai/threats/technologies/github-com-nats-io-nats-server-v2). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-27571 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-27571 being exploited in the wild.

**How severe is CVE-2026-27571?** Low severity, with a CVSS score of 3.1, published 25 February 2026.

**Which products and versions are affected?** github.com/nats-io/nats-server (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.4.1; github.com/nats-io/nats-server/v2 (Go) SEMVER:introduced=0,fixed=2.11.12, SEMVER:introduced=0,fixed=2.11.12,introduced=2.12.0-RC.1,fixed=2.12.3.

**Is there a fix for CVE-2026-27571?** Yes. github.com/nats-io/nats-server/v2 (Go): upgrade to 2.11.12, 2.12.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-27571?** Check whether you run github.com/nats-io/nats-server (Go) or github.com/nats-io/nats-server/v2 (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/nats-io/nats-server/v2 (Go): upgrade to 2.11.12, 2.12.3 or later

  ```sh
  go get github.com/nats-io/nats-server/v2@v2.12.3
  ```


## Affected products

- github.com/nats-io/nats-server (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.4.1
- github.com/nats-io/nats-server/v2 (Go) SEMVER:introduced=0,fixed=2.11.12, SEMVER:introduced=0,fixed=2.11.12,introduced=2.12.0-RC.1,fixed=2.12.3

## Identifiers

- CVE-2026-27571
- GHSA-qrvq-68c2-7grw
- GO-2026-4533

## Related threats

- [GO-2026-4833 - NATS is vulnerable to MQTT hijacking via Client ID in github.com/nats-io/nats-server](https://junglewise.ai/threats/cve-2026-33215-nats-is-vulnerable-to-mqtt-hijacking-via-client-id)
- [NATS Server: Incomplete Stripping of Nats-Request-Info Header Allows Identity Spoofing](https://junglewise.ai/threats/cve-2026-33223-nats-server-incomplete-stripping-of-nats-request-info-header)
- [GO-2026-4830 - NATS: Leafnode connections allow spoofing of Nats-Request-Info identity headers in github.com/nats-io/nats-server](https://junglewise.ai/threats/cve-2026-33246-nats-leafnode-connections-allow-spoofing-of-nats-request-info)
- [GO-2026-4832 - NATS JetStream has an authorization bypass through its Management API in github.com/nats-io/nats-server](https://junglewise.ai/threats/cve-2026-33222-nats-jetstream-has-an-authorization-bypass-through-its-management)
- [NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching](https://junglewise.ai/threats/cve-2026-33248-nats-has-mtls-verify-and-map-authentication-bypass-via-incorrect)